The present invention relates to an arrangement of the combustion chamber surfaces of an internal combustion engine, in which these surfaces exhibit at least partially a thin surface layer which will influence the octane/cetane rating requirement of the engine so as to limit the knocking tendency of the engine. An arrangement of this kind is proposed in Swedish Patent Specification No. 85 05 302-3, this known arrangement being characterized in that when at least a part of the walls of combustion chamber are treated in the manner prescribed, the walls will absorb 90-95% of all thermal radiation in the energy-rich wave length range of interest for influencing engine combustion. Furthermore, since the radiation which is reflected into the combustion chamber is diffuse, radiation from the walls of the combustion chamber contributes towards the occurrence of knocking in the combustion process to only a very slight extent.
As the energy-rich radiation is absorbed into the combustion chamber walls it converts, however, to so-called joule's heat within the thin layer of material, which is therewith heated rapidly to such high temperatures as to eventually form a so-called "hot spot" during the combustion process, which initiates knocking. Some of this radiation is also reflected back into the combustion chamber as a result of the high surface temperatures that prevail, resulting in heat loss.
The object of the present invention is to provide an improved arrangement of the aforesaid kind in which the aforementioned drawbacks are fully or partially eliminated.